Objective: To describe the prevalence of spondyloarthritis (SpA) and subtypes diagnosed prior to delivery in a nationwide population of pregnant women, and to estimate how SpA was associated with adverse pregnancy-related outcomes. Methods: Using the Danish Medical Birth Register, we identified 1,199,610 singleton pregnancies (1997–2016). Information on SpA and related subtypes (ankylosing spondylitis, psoriatic arthritis, reactive arthritis, arthritis associated with inflammatory bowel diseases, and undifferentiated SpA) was derived from the Danish National Patient Registry. Odds ratios were calculated using logistic regression models. The analyses were performed with overall SpA as exposure and stratified by subtype. Results: The overall prevalence of SpA diagnosed prior to delivery was 0.31%, increasing from 0.1% in 1997 to 0.6% in 2016. Comparing women without SpA to women with SpA, the adjusted odds ratios were increased for moderately preterm birth (OR adj 1.56 [95% confidence interval (95% CI) 1.33–1.83]), very preterm birth (OR adj 1.47 [95% CI 1.04–2.08]), elective cesarean section (OR adj 1.44 [95% CI 1.26–1.64]), emergency cesarean section (OR adj 1.17 [95% CI 1.04–1.33]), and use of epidural (OR adj 1.11 [95% CI 1.02–1.20]). The odds ratios for small for gestational age birth and preeclampsia were not increased for women with SpA compared to controls. Results were comparable for the subtypes of SpA. Conclusion: Pregnancies in women with SpA were more often complicated by adverse pregnancy outcomes than pregnancies in women without SpA. Clinicians should be aware of this when advising women with SpA in their childbearing years. Future research should focus on investigating causal relations and possible interventions aimed at preventing these outcomes.